In modern motor vehicles, airbags form part of the restraint systems which are present as standard equipment. The airbag may be a plastic bag which is connected to a gas generator which serves to inflate the airbag in an accident. The gas generator in turn is triggered via sensors which normally react to high acceleration values, as may be present in the event of accidents. For safety reasons, it is desirable that the inflation of the airbag takes place very rapidly, for example within 20-50 ms after the start of the accident. This may be achieved via pyrotechnical gas generators, and alternatively with cold gas generators or hybrid gas generators. In addition to front airbags which are accommodated in the steering wheel and/or in the dashboard in front of the driver or passenger, some vehicles are also provided with side airbags. Side airbags are deployed between the door cladding and the seat, and serve to protect the side of the occupant adjacent the door. The side airbag may be accommodated inside the seat, commonly in the seat backrest. For reasons including aesthetics, the side airbag may be concealed below a cover of the seat backrest which also covers the seat cushion. The cover may also be called an outer cover.
In the event of an accident, the airbag is forced through a tear seam of the outer cover provided therefor, deploying outwardly. Before deployment, the tear seam connects two parts of the outer cover. The tear seam is designed to tear in the presence of forces which act when the airbag is deployed. A concern is that the tear seam is located in a region which in spatial terms is relatively narrowly defined as regards the airbag, whilst said airbag attempts to expand in all directions. The latter is undesirable in that it may lead to the airbag being forced into the cushion body of the seat, for example, or a different region where it is ineffective in terms of safety. Even when the airbag is forced through the tear seam, an expansion in other directions may result in the expansion into the safety-relevant region between the door cladding and the seat being delayed, so that optimal protection of the occupant is no longer able to be ensured.
In order to counteract this, therefore, so-called force concentrators are used in order to deflect the expansion of the airbag in the direction of the tear seam and/or to concentrate the expansion force onto the tear seam. Such force concentrators normally predominantly surround the airbag and include a material having low expandability which counteracts the forces present during the expansion of the airbag. The force concentrator is opened in the direction of the tear seam, whereby a direction of expansion for the airbag is predetermined. In many cases, the ends of the force concentrator on opposing sides of the tear seam are connected (for example stitched) to the cover so that during the expansion they tear apart the cover at the tear seam and thus cause the tearing of the tear seam.
U.S. Pat. No. 6,045,151 A discloses a seat cushion sub-assembly comprising a cushion which is supported by a frame as well as a cover which surrounds this seat cushion sub-assembly and has at least one seam. An airbag is attached with an inflation unit to the frame and is partially covered by the cushion and the cover. A cover element covers the airbag in order to hold the airbag in a folded position. A seam of the cover is aligned with the airbag such that the airbag is able to tear this seam when deployed. An approximately tubular force concentrator surrounds the cover element and the airbag. The force concentrator includes a layered, flexible material which is able to resist the pressure of the airbag during inflation and is connected with two opposing ends to the cover, for example by stitching. When the airbag is inflated, the force is oriented in the direction of the seam by the force concentrator, so that said seam tears.
U.S. Pat. No. 5,967,603 A discloses a vehicle seat having a frame element, an airbag attached thereto and an outer cover which surrounds the frame element and the airbag and has a predetermined tear line. A force concentrator is connected to the outer cover in the vicinity of the predetermined tear line. The force concentrator has two parts made of material which is flexible but not expandable. Said parts have proximal ends which on opposing sides of the predetermined tear line are connected to the outer cover and extend therefrom below the outer cover in opposing directions to the distal ends. The two parts are fastened to one another at these distal ends by complementary fastening means, such that they form a sleeve enclosing the airbag and the frame member.
A device for a vehicle seat is disclosed in FR 2 940 212 A3, said device comprising at least one airbag module and a force concentrator which serves to deflect the airbag in a predetermined region. In this case, the force concentrator and the airbag module are arranged adjacent to a support structure and secured, for example, by a screw and nut. The force concentrator may include the same material as the airbag and has a predetermined tear seam, said force concentrator being secured by means of a hook and loop fastener in the vicinity of said tear seam to a foam block of the vehicle seat.
FR 2 978 712 B1 discloses a backrest of a vehicle seat having a side airbag. In this case, an airbag module and a force concentrator which are screwed to a support structure are also provided. The force concentrator which surrounds the airbag module in the manner of a jacket has two adjacent ends which are arranged in the vicinity of a predetermined tear seam of an outer sleeve of the vehicle seat. The aforementioned ends in this case are connected via rapid fasteners to the parts of the outer sleeve adjacent to the predetermined tear seam, wherein the rapid fasteners may be configured as hook and loop fasteners, hooks or buttons.
DE 10 2011 105 461 A1 discloses a vehicle seat having a structural part, a cushion body as well as a cover which covers the cushion body and which has two cover parts connected together in a tear seam. Moreover, an airbag module is received in an airbag pocket which serves as a force concentrator and which is fastened with its two ends in the region of the tear seam to the cover. In order to prevent the airbag from being forced into the cushion body, a protective strip made of flexible tear-resistant material is also fastened between the airbag pocket and the cover.
DE 10 2006 053 601 A1 discloses a vehicle seat device having a frame, a seat cushion arranged in the vicinity thereof as well as a cladding cover which has a seam on one side of the seat. Moreover, an airbag module is provided with an airbag. A housing, the airbag being able to expand therein and having a tear seam, is enclosed by a force concentrator with two panels. The ends of the panels are fastened to the seam of the cladding cover, whereby they exert a force on this seam when the airbag is triggered.
In view of the prior art set forth, the rapid and reliable deployment of an airbag accommodated inside a vehicle seat leaves further room for improvement.